Golf club head

ABSTRACT

An iron-type golf club head is disclosed having a heel portion, a sole portion, a toe portion, a top-line portion, a front portion, a rear portion, and a striking face. A back wall is also disclosed in the rear portion enclosing a portion of the rear portion to create an enclosed cavity. The cavity is defined by at least a rear surface of the striking face, an inner back wall surface, and the sole portion. A plug and a filler material is located within the enclosed cavity. The filler material surrounds the plug and is configured to hold the plug in place. The plug is lighter than the filler material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation reissue application of reissueapplication Ser. No. 15/904,245, filed on Feb. 23, 2018, now U.S. Pat.No. RE47,653, which is an application for reissue of U.S. Pat. No.9,265,995, issued Feb. 23, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/960,554, filed on Aug. 6, 2013, now U.S. Pat.No. 8,814,725, which is a division of application Ser. No. 13/709,876,filed Dec. 10, 2012, now U.S. Pat. No. 8,517,863, which is acontinuation of application Ser. No. 13/327,638, filed Dec. 15, 2011,now U.S. Pat. No. 8,328,663, which is a continuation of application Ser.No. 12/462,198, filed on Jul. 29, 2009, now U.S. Pat. No. 8,088,025.

FIELD

The present disclosure relates to a golf club head. More specifically,the present disclosure relates to a golf club head filled with adampening material.

BACKGROUND

A golf set includes various types of clubs for use in differentconditions or circumstances in which a ball is hit during a golf game. Aset of clubs typically includes a “driver” for hitting the ball thelongest distance on a course. A fairway “wood” can be used for hittingthe ball shorter distances than the driver. A set of irons are used forhitting the ball within a range of distances typically shorter than thedriver or woods.

An iron has a flat face that normally contacts the ball whenever theball is being hit with the iron. Irons have angled faces for achievinglofts ranging from about 18 degrees to about 60 degrees.

Every club has a “sweet spot” that represents the best hitting zone onthe face for maximizing the probability of the golfer achieving the bestand most predictable shot using the particular club. Most golfers striveto make contact with the ball inside the sweet spot to achieve a desiredtrajectory. However, a golf club head may have a tendency to causeundesirable sounds and vibrations upon impact.

SUMMARY OF THE DESCRIPTION

The present disclosure describes a golf club head comprising a heelportion, a toe portion, a crown, a sole, and a face.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

According to one aspect of an embodiment of the present invention, ahollow iron-type golf club head is described including a heel portion, asole portion, a toe portion, a top-line portion, a front portion, a rearportion, and a striking face. A back wall is located in the rear portionenclosing a substantial portion of the rear portion to create asubstantially enclosed cavity. The enclosed cavity is defined by atleast a rear surface of the striking face, an inner back wall surface,and the sole portion. At least one plug and a filler material locatedwithin the enclosed cavity are described. The filler materialsubstantially surrounding the plug and is configured to hold the atleast one plug in place.

In one example, the enclosed cavity has a volume between about 1 cc and200 cc and an unsupported face area between about 300 mm² to about 4,000mm² is described.

In another example, the unsupported face area includes a thickenedcentral region and the plug is positioned to be in contact with at leasta portion of the thickened central region. The at least one plugcontacts the inner back wall surface.

In yet another example, the striking face includes a welded strikingplate and a total striking face area is between about 2,700 mm² and5,000 mm².

In one example, an aperture into the enclosed cavity is provided forfilling the cavity with the filler material. The filler material is anexpanding foam material having a density between about 0.03 g/cc andabout 0.19 g/cc.

In another example, the filler material occupies about 50% to about 99%of the total enclosed cavity volume. The filler material completelyfills a remaining cavity volume around the at least one plug. The fillermaterial contacts an entire first side surface of the at least one plug.

In yet another example, the filler material and the at least one plughave a combined weight of less than about 10 g or about 5 g.

In one example, the filler material and plug have a combined weight ofless than about 20% of the total club head weight, or less than about5%.

In another example, the back wall includes a first aperture having atleast a first diameter and a slot configured to match at least a keyingportion of the at least one plug and the coefficient of restitution ofthe club is greater than about 0.8.

In yet another example, the striking face includes a striking plateformed of a steel, such as maraging steels, maraging stainless steels,and PH stainless steels.

In one example, the plug is in direct contact with a rear surface of thestriking face and at least a portion of the filler material is in directcontact with a rear surface of the striking face.

In another example, the back wall includes at least a first aperture.The first aperture is configured to allow the at least one plug to beinserted into the first aperture and is configured to allow the at leastone plug to move from a first position to a second position.

In yet another example, the back wall includes at least one slot, the atleast one slot being connected to the first aperture and is configuredto secure the at least one plug.

According to one aspect of one embodiment of the present invention, amethod of manufacturing a hollow iron-type golf club with a plug andfiller material is described. A body including a heel portion, a soleportion, a toe portion, a top-line portion, a front portion, and a rearportion having a back wall is disclosed. An aperture is formed on thebody. A striking face is formed and attached to the front portion of thebody to form a cavity defined by a rear surface of the striking face, aninner surface of the back wall, and the sole portion. At least one plugis inserted into the aperture. The at least one plug is in directcontact with the rear surface of the striking face and the inner surfaceof the back wall. The plug is moved from a first position to a secondposition. A filler material is inserted into the aperture. The fillermaterial substantially surrounds the plug and is configured to hold theplug in place. The aperture is covered with a badge in the rear portionof the body.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in winch likereferences indicate similar elements.

FIG. 1A is a front view of an embodiment of a golf club head.

FIG. 1B is a cross-sectional view taken along section lines 1B-1B inFIG. 1A.

FIG. 1C is a magnified view of DETAIL 1C in FIG. 1B.

FIG. 1D is an elevated toe perspective view of a golf club head.

FIG. 1E is a cross-sectional view taken along section lines 1E-1E inFIG. 1D.

FIG. 2A is an exploded assembly view of a golf club head according to anembodiment.

FIG. 2B is an assembled view of a golf club head according to anembodiment.

FIG. 3A is a front view of another embodiment of a golf club head.

FIC. 3B is a cross-sectional view taken along section lines 3B-3B inFIG. 3A.

FIG. 4 is a rear view of a golf club head according to an embodiment.

FIG. 5A is an isometric view of a golf club head insert.

FIG. 5B is an isometric view of a golf club head insert.

FIG. 6A illustrates an exploded assembly view of a golf club headaccording to an embodiment.

FIG. 6B illustrates an assembled view of a golf club head according toan embodiment.

FIG. 7 illustrates a flow chart of a golf assembly operation.

FIG. 8 illustrates a graph of a frequency response of exemplary golfclub heads.

DETAILED DESCRIPTION

Various embodiments and aspects of the inventions will be described withreference to details discussed below, and the accompanying drawings willillustrate the various embodiments. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentinvention. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present inventions.

FIG. 1A illustrates a hollow iron golf club head 100 including a heel102, toe 104, sole portion 108, and top line portion 106. The strikingface 110 includes grooves 112 that are designed for impact with the golfball. In some embodiments, the golf club head 100 can be a singleunitary cast piece, while in other embodiments, a striking plate can beformed separately to be adhesively or mechanically attached to the golfclub head 100.

FIGS. 1A and 1D also show a center point 101 being an ideal strikingpoint in the center of the striking face 110 and respective orthogonalCG axes. A CG x-axis 105, CG y-axis 107, and CG z-axis 103 intersect atthe center point 101. In addition, a CG z-up axis 109 is defined as anaxis perpendicular to the ground plane 111 and having an origin at theground plane 111. The ground plane 111 is assumed to be a perfectly flatplane.

In certain embodiments, a desirable CG-x location is between about 5 mm(heel side) and about −5 mm (toe side) along the CG x-axis 105. Adesirable CG-y location is between about 0.25 mm to about 20 mm alongthe CG y-axis 107 toward the rear portion of the club head.Additionally, a desirable CG-z location is between about 12 mm to about25 mm along the CG z-up axis 109, as previously described.

FIG. 1B shows a cross sectional side view of the hollow iron golf clubhead 100 along the cross-section lines 1B-1B shown in FIG. 1A. Thecross-section lines 1B-1B are taken through an ideal striking point 101in the center of the striking face 110. The ideal striking point 101 islocated in a striking face plane 125 at the intersection of a first axis(within the face plane 125) passing through the midpoint of the longestscoreline groove and a second horizontal axis (within the face plane125) offset from the leading edge (defined as the intersection of thesole portion and the face plane 125) by a distance d of about 16.5 mmwithin the face plane 125, as shown in FIG. 1D. The striking face 110includes a front surface 110a and a rear surface 110b. The hollow irongolf club head 100 further includes a back portion 128 and a frontportion 130. The striking face 110 located in the front portion 130 hasan inverted cone profile or thickened central region that providesmultiple thicknesses across the striking face 110. The thickened centralregion can be a variety of profile shapes and is not restricted to acone shape.

The striking face 110 has a first thickness 116 and a second thickness118. The second thickness is greater than the first thickness 116. Incertain embodiments, the first thickness 116 can be between about 1.5 mmand about 2.5 mm, with a preferred thickness of about 2 mm or less. Thesecond thickness 118 can be between about 1.7 mm and about 2.5 mm orless than about 2.7 mm. Furthermore, the sole portion 108 has a solethickness dimension 140 that extends within a region between a rearprotrusion 138 and the striking face 110. In certain embodiments, thesole thickness dimension 140 is between about 1 mm and about 2 mm, orless than about 2 mm. In one embodiment, a preferred sole thickness 140is about 1.8 mm or less. A recess 134 is located above the rearprotrusion 138 in the back portion 128 of the club head. A back wall 132encloses the entire back portion 128 of the club head to define a cavity120 that is primarily filled with a filler material 121.

In one embodiment, the filler material 121 can be an expandable foamsuch as Expancel® 920 DU 40 which is an acrylic copolymer encapsulatinga blowing agent, such as isopentane. A copolymer is greater than about75 weight percent of the composition and the blowing agent is about15-20 weight percent. The unexpanded particle size of the fillermaterial 121 can be between about 2 μm and about 90 μm depending on thecontext.

In one embodiment, the density of the filler material 121 is betweenabout 0.16 g/cc and about 0.19 g/cc or between about 0.03 g/cc and about0.19 g/cc. In certain embodiments, the density of the filler material121 is in the range of about 0.03 g/cc to about 0.2 g/cc, or about0.04-0.10 g/cc. The density of the filler material 121 impacts the COR,durability, strength, and filling capacity of the club head. In general,a lower density material will have less of an impact on the COR of aclub head. The filler material 121 can have a hardness range of about15-85 Shore OO hardness or about 80 Shore OO hardness or less.

In one embodiment, the filler material 121 is subject to heat forexpansion of about 150° C.+/−10° C. for about 30 minutes. In someembodiments, the expansion of the filler material 121 can begin at about125° C. to about 140° C. A maximum expansion temperature range can bebetween about 160° C. to about 190° C. The temperature at which theexpansion of the filler material 121 begins is critical in preventingunwanted expansion after the club head is assembled. For example, afiller material that begins expanding at about 120° C. will not causeunwanted expansion when the club is placed in the trunk of a car (wheretemperatures can reach up to about 83° C.). Thus, a filler material 121that has a beginning expansion temperature of greater than about 80° C.is preferred.

Some other examples of materials that can be used as a filler materialor plug material include, without limitation: viscoelastic elastomers;vinyl copolymers with or without inorganic fillers; polyvinyl acetatewith or without mineral fillers such as barium sulfate; acrylics;polyesters; polyurethanes; polyethers; polyamides; polybutadienes;polystyrenes; polyisoprenes; polyethylenes; polyolefins;styrene/isoprene block copolymers; metallized polyesters; metallizedacrylics; epoxies; epoxy and graphite composites; natural and syntheticrubbers; piezoelectric ceramics; thermoset and thermoplastic rubbers;foamed polymers; ionomers; low-density fiber glass; bitumen; silicone;and mixtures thereof. The metallized polyesters and acrylics cancomprise aluminum as the metal. Commercially available materials includeresilient polymeric materials such as Scotchdamp™ from 3M, Sorbothane®from Sorbothane, Inc.. DYAD and GPS from Soundcoat Company Inc., Dynamatfrom Dynamat Control of North America, Inc., NoViFlex™ Sylomer® fromPole Star Maritime Group, LLC, Isoplast® from The Dow Chemical Company,and Legetolex™ from Piqua Technologies, Inc. In one embodiment thefiller material may have a modulus of elasticity ranging from about0.001 GPa to about 25 GPa, and a durometer ranging from about 5 to about95 on a Shore D scale. In other examples, gels or liquids can be used,and softer materials which are better characterized on a Shore A orother scale can be used. The Shore D hardness on a polymer is measuredin accordance with the ASTM (American Society for Testing and Materials)test D2240.

FIG. 1B further shows an optional ridge 136 extending across a portionof the outer back wall surface 132a forming an upper concavity and alower concavity. An inner back wall surface 132b defines a portion ofthe cavity 120 and forms a thickness between the outer back wall surface132a and the inner back wall surface 132b. In some embodiments, the backwall thickness varies between a thickness of about 1 mm to about 3 mm.

FIG. 1C is a magnified view of the top line 106 DETAIL 1C shown in FIG.1B. FIG. 1C shows the top line 106 and a striking plane 125 that isparallel to and contains the front striking surface 110. A second plane127 is shown being perpendicular to the striking plane 125 and thestriking surface 110. The top line 106 includes a return surface 123immediately adjacent to the striking face 110 in the top line portion106. The return surface 123 extends from the striking face 110 towardthe back portion 128 and a majority of the return surface 123 isgenerally parallel with the second plane 127. A transition surface 126connects the return surface 123 to the outer back wall surface 132a.

In certain embodiments, the return surface 123 extends from the strikingface 110 a return distance 124 (or “effective top line thickness”) ofbetween about 3.5 mm and 5 mm, or about 4.8 mm or less, as measuredalong the second plane 127 and perpendicular to the striking plane 125.In some embodiments, the return surface 123 extends less than 60% of thetotal top line thickness 122. In certain embodiments, the total top linethickness 122 is between about 6 mm and about 9 mm, or about 8.5 mm orless, as measured along the second plane 127 and perpendicular to thestriking plane 125.

A small effective top line thickness 124 of the return surface 123creates the perception to a golfer that the entire top line 106 of theclub head 100 is thin. A perceived thin top line 106 can enhance theaesthetic appeal to a golf player.

FIG. 1D illustrates an elevated toe view of the golf club head 100including a back portion 128, a front portion 130, a sole portion 108, atop line portion 106, and a striking face 110, as previously described.

FIG. 1E illustrates a cross-sectional view taken along cross-sectionallines 1E-1E of FIG. 1D. FIG. 1E shows a rear unsupported face region146, an inverted cone technology region 148 (hereinafter, “ICT region”or “Thickened Central Region”) and a rear supported face region 150. Theunsupported face region 146 is a region of the striking face 110 wherethe thickness of the face is thin (i.e. less than about 3 mm or lessthan about 5 mm) and is not supported by any separate or integratedmetallic structure having a significant impact on the stiffness of thestriking face 110. The ICT region 148 can be considered a sweet spotwhere an ideal impact can occur at the center point 152 of the ICT.Variable thickness configurations or inverted cone configurations arediscussed in, for example, U.S. Pat. Nos. 6,800,038, 6,824,475,6,904,663, and 6,997,820, all incorporated herein by reference.

The rear supported face region 150 is located about a periphery of theunsupported face region 146. The inverted cone region 148 is centeredabout an ideal impact location 152 located in a central location of theunsupported face region 146. The inverted cone region 148 includes anouter span 144 and an inner span 142. In some embodiments, the outerspan 144 is between about 15 mm and about 25 mm, or at least 20 mm. Theinner span 142 of the inverted cone region 148 represents the thickestportion of the unsupported face region 146. Inn certain embodiments, theinner diameter 142 is between about 5 mm and about 15 mm, or at leastabout 10 mm.

The tabulated values in Tables 1-7 are total face area, thin facethickness, thickened central region (or ICT region area), and theunsupported surface area.

The “total face area” is defined as the area of face contained within aface plane on a front striking portion of the club head. The “thin facethickness” is the nominal thickness of the striking surface in itsthinnest location (such as dimension 116, in FIG. 1B). The ICT region148 area is the surface area contained by the variable thickness regionor inverted cone area. Furthermore, the “Unsupported Surface Area” isthe unsupported rear surface area 146 of the striking face (including anICT region 148).

EXAMPLE 1

TABLE 1 Thickened Central Total Thin Face Region Unsupported Face AreaThickness Area Surface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron2,825 2.1 541 2,175 6-iron 2,964 2.1 541 2,276 9-iron 3,116 2.1 5412,094 Wedge 3,452 2.1 541 2,345

EXAMPLE 2

TABLE 2 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 2,824 2.4 527 2,4036-iron 2,962 2.4 527 2,473 9-iron 3,113 2.4 527 2,245 Wedge 3,451 2.4527 2,540

EXAMPLE 3

TABLE 3 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 2,792 2.5 388 1,6316-iron 2,965 2.5 388 1,608 9-iron 3,151 2.5 388 1,597 Wedge 3,304 2.5388 1,519

EXAMPLE 4

TABLE 4 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 2,796 2.2 247 1,5606-iron 2,934 2.2 247 1,529 9-iron 3,084 2.4 247 1,479 Wedge 3,421 2.4247 1,711

EXAMPLE 5

TABLE 5 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 2,763 2.4 314 2,2206-iron 2,974 2.4 314 2,206 9-iron 3,376 2.4 314 2,240 Wedge 3,421 2.4314 2,055

EXAMPLE 6

TABLE 6 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 2,790 2.5 239 1,5676-iron 2,958 2.5 292 1,719 9-iron 3,150 2.5 308 1,621 Wedge 3,301 2.5313 1,627

EXAMPLE 7

TABLE 7 Total Thin Face ICT Unsupported Face Area Thickness RegionSurface Club head (mm²) (mm) (mm²) Area (mm²) 3-iron 3,177 2.0 700 3,1756-iron 3,231 2.0 700 3,260 9-iron 3,384 2.0 315 2,244 Wedge 3,436 2.0315 2,104

The tabulated values are representative and other configurations can beprovided as described herein. It should be noted, in the above examples,one advantage of the Unsupported Surface Area is that a mass savings isachieved while also providing a durable and high COR striking face.

In the examples provided in Tables 1-7, a total face area can be in arange of about 2,700 mm² to about 4,000 mm². The Unsupported SurfaceArea can be within a range of about 300 mm² to about 4,000 mm², orpreferably 450 mm² to about 3,500 mm². In some embodiments, theUnsupported Surface Area is at least greater than about 2,000 mm². Thethin face thickness can be within a range of about 1.0 mm-3.0 mm,preferably 1.5-2.5 mm, and also preferably in a range of about 1.6-2.0mm. In certain embodiments, the thin face thickness is less than about2.0 mm. In embodiments having an ICT region, the ICT region surface areacan range from about 230 mm² to about 2,000 mm².

FIG. 2A illustrates one embodiment of a hollow iron golf club head 200having a top line portion 206, a toe portion 204, a heel portion 202, arear portion 222, and a sole portion 208. The golf club head 200includes a back wall 212 located within a cavity region 216 or recess inthe rear portion 222 of the club head 200. The cavity region 216includes side walls around a periphery of the back wall 212 creating afirst recess or cavity region 216 where a badge 214 can be inserted andadhesively attached to the back wall 212. An aperture 210 is located inthe back wall 212 and can be used for filling the hollow iron 200 with asound dampening filler material 224 as previously described. A secondrecess 220 is located below the first recess 216 and can also beconfigured to receive a second badge.

After the hollow iron 200 is filled with the filler material 224, thebadge 214 is adhesively or mechanically attached to the back wall 212 tocover or occlude the aperture 210 to prevent filler material fromleaving the cavity and also to achieve a desired aesthetic and furtherdampening.

FIG. 2B shows the golf club head 200 fully assembled after the fillermaterial 224 is inserted and the badge 214 is attached to the back wall212.

FIG. 3A illustrates another embodiment of a golf club head 300 includinga heel portion 302, a toe portion 304, a top line portion 306, a soleportion 308, a body portion 309 and a striking plate 310 located on astriking surface. The striking plate 310 includes grooves 314.

In one embodiment, the striking plate 310 is mechanically attached to afront portion of the body portion 309. Specifically, a weld line 312 isformed about a periphery of the striking plate 310.

The weld is created by a welding device, such as a laser or plasma weld.In one embodiment, the weld is applied on the front face of the golfclub head 300 from a frontward to rearward direction. The weld can beany type of weld including (but not limited to) bead, groove, fillet,surfacing, tack, plug, slot, friction, and resistance welds.

Compared to TIG welding and other welding techniques, laser welding canbe advantageous by concentrating more energy at the weld site. Laserwelding also produces a smaller heat affected zone and more localizedmelt, less material interdiffusion, and reduced material fatigue duringsubsequent use.

After completion of the welding, the club head is subjected to a heattreatment for aging. The post-weld heat treatment is generally at480-540° C. for four hours. The club head is also machine finished asrequired, such as grinding, polishing, or sandblasting, to smooth andtopologically blend the surface of the weldment into the face plane.Finish machining is desirably followed by passivation. After completingfinish-machining, it may be desirable to apply a suitable surfacetreatment of the club head, such as plating, painting, coating, or thelike. Plating may be performed to produce a surface plating layer thatprotects against corrosion and is strong, durable, relatively inert, andaesthetically pleasing. Exemplary materials for forming a plating layerare Cr, Ni, and Cu. Exemplary techniques for forming the plating layerare electrode plating, electroless plating, physical vapor deposition(PVD), chemical vapor deposition (CVD), ion plating, andion-beam-enhanced diffusion. An intermediate sublayer can be appliedprior to the plating layer such as soft nickel, soft copper, and oxides.

In some embodiments, the COR is greater than 0.790. Preferably, the CORis at least 0.80 as measured according to the USGA Rules of Golf basedon a 160 ft./s ball speed test and the USGA calibration plate. The CORcan even be as high as 0.83.

In certain embodiments, the striking plate 310 can be formed of forgedmaraging steel, maraging stainless steel, or precipitation-hardened (PH)stainless steel. In general, maraging steels have high strength,toughness, and malleability. Being low in carbon, they derive theirstrength from precipitation of inter-metallic substances other thancarbon. The principle alloying element is nickel (15% to nearly 30%).Other alloying elements producing inter-metallic precipitates in thesesteels include cobalt, molybdenum, and titanium. In one embodiment, themaraging steel contains 18% nickel. Maraging stainless steels have lessnickel than maraging steels but include significant chromium to inhibitrust. The chromium augments hardenability despite the reduced nickelcontent, which ensures the steel can transform to martensite whenappropriately heat-treated. In another embodiment, a maraging stainlesssteel C455 is utilized as the striking plate. In other embodiments, thestriking plate is a precipitation hardened stainless steel such as 17-4,15-5, or 17-7.

The striking plate can be forged by hot press forging using any of thedescribed materials in a progressive series of dies. After forging, thestriking plate is subjected to heat-treatment. For example, 17-4 PHstainless steel forgings are heat treated by 1040° C. for 90 minutes andthen solution quenched. In another example, C455 or C450 stainless steelforgings are solution heat-treated at 830° C. for 90 minutes and thenquenched.

In one embodiment, the body portion 309 is made from 17-4 steel. Howeveranother material such as carbon steel (e.g., 1020, 1030, 8620, or 1040carbon steel), chrome-molybdenum steel (e.g., 4140 Cr—Mo steel), Ni—Mosteel (e.g., 8620 Ni—Cr—Mo steel), austenitic stainless steel (e.g.,304, N50, or N60 stainless steel (e.g., 410 stainless steel) can beused.

The components of the described components disclosed in the presentspecification can be formed from any of various suitable metals or metalalloys.

In addition to those noted above, some examples of metals and metalalloys that can be used to form the components of the parts describedinclude, without limitation: titanium alloys (e.g., 3-2.5, 6-4, SP700,15-3-3-3, 10-2-3, or other alpha/near alpha, alpha-beta, and beta/nearbeta titanium alloys), aluminum/aluminum alloys (e.g., 3000 seriesalloys, 5000 series alloys, 6000 series alloys, such as 6061-T6, and7000 series alloys, such as 7075), magnesium alloys, copper alloys, andnickel alloys.

The body portion 309 can include various features such as weightingelements, cartridges, and/or inserts or applied bodies as used for CGplacement, vibration control or damping, or acoustic control or damping.For example, U.S. Pat. No. 6,811,496, incorporated herein by referencein its entirety, discloses the attachment of mass altering pins orcartridge weighting elements.

After forming striking plate 310 and the body portion 309, the strikingplate 310 and body portion 309 contact surfaces can be finish-machinedto ensure a good interface contact surface is provided prior to welding.In one embodiment, the contact surfaces are planar for ease of finishmachining and engagement.

The thickness profiles and low thickness values of the striking platecan be achieved during the forging of the striking plate. In oneembodiment, a 0.3 mm to 1.0 mm machine stock plate can be added to thestriking plate to increase tolerance control. After forging, thestriking plate can be slightly milled and engraved with score-lines. Akey advantage of being able to forge such a thin face is the freeing upof discretionary mass (up to about 20 g) that can be placed elsewhere inthe club head (such as the rear piece) for manipulation of the moment ofinertia or center of gravity location.

The thickness of the striking plate in the thin face area is generallyconsistent in thickness and non-variable. Of course, manufacturingtolerances may cause some variation in the thin face area. The thin facearea and the ICT region can be considered the “unsupported” face area ofthe striking face because the thickness dimensions are relatively thinin those areas. In certain embodiments, the thin face area is about 50%or more of the unsupported surface area.

FIG. 3B illustrates a cross-sectional view taken along cross sectionlines 3B-3B shown in FIG. 3A. FIG. 3B further shows the front portion330 and the back portion 328 in addition to the sole portion 308 and topline portion 306. The welded striking plate 310 includes a thickenedcentral region 334, a first thickness 316, and a second thickness 318 aspreviously described. The sole portion 308 includes a minimum solethickness 326 of about 2 mm or less, or within the ranges describedherein, such as about 1 mm to about 2 mm or less than 3 mm.

A filler material 324 fills an entire interior cavity 332 and surroundsa plug 320 located near or at least in partial contact with thethickened central region 334. It is understood that more than one plug320 can be provided. In certain embodiments, a plurality of plugs suchas two, three, or four plugs can be used. The plug 320 includes a firstsurface (or first side surface) 320a contacting the filler material 324.The filler material 324 directly contacts the entire first surface 320ato hold and prevent the plug 320 from shifting out of position. In otherwords, the filler material 324 completely surrounds the plug 320 withina plane parallel to the striking plate 310. A second surface 320b of theplug 320 directly contacts at least a portion of the inverted coneregion or thickened region 334 of the striking plate 310. Furthermore, athird surface 320c of the plug 320 directly contacts at least a portionof a back wall 336. In other words, the filler material 324 does notsurround the plug 320 within a plane perpendicular to the striking plate310. The back wall 336 includes an inner back wall and an outer backwall having certain dimensional thicknesses as previously described.

An aperture 338 is located in the back wall 336 to allow the plug 320 tobe inserted into the fully enclosed cavity 332. Upon insertion throughthe aperture 338, the plug is compressed slightly so that a frictionalengagement occurs between the second surface 320b of the plug and therear surface of the striking plate 310. In addition, a frictionalengagement also occurs between the third surface 320c of the plug and aportion of the back wall 336. Optionally, the aperture 338 can belocated anywhere on the club head body surface other than the frontstriking face. For example, the aperture 338 can be located on the sole,toe, heel, or top line surfaces.

After the plug 320 is frictionally engaged in a position, the fillermaterial 324 can be inserted into the cavity 332. In certainembodiments, the plug 320 is a polymeric material.

In one embodiment, the plug 320 material is a urethane or siliconematerial having a density of about 0.95 g/cc to about 1.75 g/cc, orabout 1 g/cc. The plug 320 can have a hardness of about 10 to about 70shore A hardness. In certain embodiments, a shore A hardness of about 40or less is preferred. In certain embodiments, a shore D hardness of upto about 40 or less is preferred.

The filler material 324 can be an expanding foam material that isexpanded by a certain amount of heat as previously described. The fillermaterial 324 expands and fills a relatively large volume, greater thanthe volume occupied by the plug 320. In some embodiments, the volume ofthe cavity 332 is between about 1 cc and about 200 cc, or preferablybetween about 10 cc and about 20 cc. For the purposes of measuring thecavity 332 volume herein, the aperture 338 is assumed to be removed fromthe back wall 336 and an imaginary continuous back wall 336 orsubstantially planar back wall is utilized to calculate the cavityvolume.

In some embodiments, the filler material 324 occupies about 50% to about99% of the total club head cavity volume while the ping 320 occupiesbetween about 0% to about 20% of the total cavity volume. In specificembodiments, the plug 320 occupies between about 0.1 cc and 1 cc withthe remainder of the cavity volume being filled by the filler material324. It is understood that any of the embodiments described herein canbe provided without a plug and filler material only.

In order to achieve a desirable CG location, the filler material 324 andplug 320 must be lightweight. In certain embodiments, the total mass ofthe filler material 324 and plug 320 is less than about 5 g or betweenabout 2 g and about 4 g. In one embodiment, the total weight of thefiller material 324 and the plug 320 is 10 g or less, or about 3 g orless. In certain embodiments, the total weight of the filler material324 and plug 320 is less than 2% of the total weight of the club head300 (excluding any badges, filler material/plug, and ferrule ring). Inother embodiments, the total weight of the filler material 324 and plug320 is less than about 10% of the total weight of the club head 300.

Table 8, shows exemplary golf club heads and the respective weightratios between the filler material 324 and plug 320 and the total clubhead weight 300, as described above.

EXAMPLE 8

TABLE 8 Total Weight of Filler Total Weight of Weight Ratio Club headMat. And Plug (g) Club Head (g) (%) 3-iron 3.7 229.9 1.6 4-iron 3.6236.1 1.5 5-iron 3.6 242.1 1.5 6-iron 3.5 248.5 1.4

As shown in Table 8, the total weight of the filler material 324 andplug 320 is between about 1% and about 5% of the total weight of theclub head (excluding the badges, filler material/plug, and ferrulering). Thus, a desirable CG location is still attainable while improvingthe sound and feel of the golf club head. In certain embodiments, theplug 320 can weigh about 0.5 g to about 1 g and the filler material canweigh about 5 grams or less. In some embodiments, the plug 320 weighsabout 0.7 g or less. fit other embodiments, the plug 320 can be equal toor heavier than the total filler material weight.

In yet other embodiments, the filler material 324 and the plug 320 havea combined weight of less than 20% of the total club head weight(excluding badges, filler material/plug, and ferrule ring). In oneembodiment, the combined weight of the filler material 324 and plug 320is less than 5%.

FIG. 4 illustrates a rear view of an exemplary embodiment of a golf clubhead 400 including a heel portion 402, a toe portion 404, a top lineportion 406, a sole portion 408, and a back wall 410. FIG. 4 furthershows an aperture 414 having an aperture diameter 420 of about 10 mm toabout 15 mm, or less than 30 mm. The aperture 414 is connected with aslot 412 that extends away from the aperture 414 in a horizontaldirection toward the heel portion 402. The aperture 414 has an openingat the slot connection portion and is configured to allow a plug 422 tomove from a first position to a second position.

It is understood that the slot 412 could extend in the oppositehorizontal direction toward the toe region 404 or in any directionneeded. The slot includes a rounded end portion 418 having a diameterbetween about 2 mm to 5 mm, or preferably about 3 mm.

A sliding distance 416 defines the distance between a first center point424 of the aperture 414 to a second center point 426 of the rounded endportion 418. In certain embodiments, the sliding, distance 416 isbetween about 1 mm and 70 mm, or between about 5 mm and about 15 mm. Inone embodiment, the sliding distance 416 is about 11 mm, the aperturediameter is about 12 mm, and the rounded end portion 418 of the slot 412is about 3 mm.

A plug 422 is initially inserted into the aperture 414 and then moved byan amount equal to the sliding distance 416. A portion of the plug 422is keyed to the slot 412 and thereby restricts the movement of the plug422 in a sole 408 to top line 406 direction.

FIG. 5A illustrates an exemplary embodiment of a plug 500. The plug 500has an overall cylindrical shape having a first surface (or side wall)502, a second surface (or bottom surface) 508, and a third surface (ortop surface) 514. In one embodiment, the side wall 502 is thecontinuous, curved, and circular wall of the cylindrical shaped plug500. The top surface 514 includes an engagement surface 504 and a keyingportion 506 that is elevated above the engagement surface 504. Thekeying portion 506 includes a raised side engagement wall 512 formingthe keying portion 506 and a recessed center portion 510. In someembodiments, the center portion 510 can be used for engagement with anapplicator during the insertion and movement of the plug 500. The tip ofan applicator can be inserted into the recessed center portion 510.

The keying portion 506 includes a center point 518 which is locatedalong a central axis 516 of the cylindrical shaped plug 500. When theplug 500 is inserted into the aperture 414, the overall diameter 520 ofthe side wall 502 of the cylindrical plug 500 is less than the diameter420 of the aperture 414 to allow easy insertion of the plug 500. Oncethe bottom surface 508 of the plug 500 engages a rear surface of thestriking plate, the plug 500 can be moved a sliding distance 416 from afirst position to a second position. The first position is characterizedby the central axis 516 of the plug 500 being aligned with the firstcenter point 424 of the aperture 414 across a plane parallel to the backwall 410. The second position is characterized by the central axis 516of the plug 500 being aligned with the second center point 426 of therounded portion 418 of the slot 412. It is understood that the plug 500is not limited to cylindrical shapes and can be cubical, rectangular,elliptical, spherical, egg shaped, pyramidal, tapered, trapezoidal, orany known three dimensional shape.

In certain embodiments, the keying portion 506 and raised sideengagement wall 512 can be eliminated, thus relying purely on thecompression of the plug to hold it in place.

When the plug 500 is moved to the second position or the engagedposition, the plug 500 is slightly compressed between the rear wall ofthe striking plate and the back wall 410. In the second position, theengagement surface 504 of the plug 500 engages the interior wall of theback wall 410. The raised side engagement wall 512 of the keying portion506 engages side walls of the slot 412 to prevent significant movementof the plug in at least a sole-to-top line direction. It is understoodthat frictional engagement between the plug 500 and the back wall 410will also reduce the amount of movement of the plug in a heel-to-toedirection, even before a filler material is introduced.

FIG. 5B illustrates another exemplary plug 522 of a general wedge shape.The wedge shaped plug 522 is configured to be compressed between therear wall of the striking plate and the back wall. A side view of theplug 522 shows a generally trapezoidal shape. The aperture 414 can beany shape including a rectangular or trapezoidal shape to accommodatethe shape of the plug 522. The wedge shaped plug 522 is inserted intothe aperture 414 and moved to a wedge position as previously described.

FIG. 6A illustrates an exploded assembly of an exemplary club head 600embodiment utilizing a plug 500 and filler material 622, as previouslydescribed. The club head 600 includes a striking face 614, an interiorrear striking face surface 616, an inverted cone or thickened centralregion 602, an aperture 608, a slot 618, a back wall surface 620, arecess 612, and a badge 610.

FIG. 6A further illustrates a heel side vent hole 604 and a toe sidevent hole 606 located in the back wall surface 620. The vent holes604,606 enables air to escape the interior cavity during the expansionprocess of the filler material 622 or expanding foam.

FIG. 6B illustrates a fully assembled club head after the plug 500 andfiller material 622 have been inserted into the interior cavity of theclub head 600. The badge 610 is inserted into the recess 612 and coversthe entire back wall surface 620 while obscuring the aperture 608, slot618, plug 500, and vent holes 604,606.

FIG. 7 illustrates a series of operations 700 that are accomplished toinserting a plug into an interior cavity of a club head. Initially, aweld is placed on the face of an iron-type golf club to attach astriking plate. A weld bead likely occurs on the front face portion andwithin a rear cavity portion of the golf club head. If the strikingplate is cast instead of welded, a weld operation on the face of theclub head is not required.

In a first operation 702, an aperture is formed in the back wall of ahollow iron. The aperture can be created through machining or casting orother manufacturing processes. A plug, as described above, is theninserted into the aperture in a second operation 704 so that the plug isprimarily located within an interior cavity of the club head.

In a third operation 706, the plug is moved from a first position to asecond position so that the plug is relatively secured in place in thesecond position. Once the plug is moved to the second position, a fillermaterial is introduced, in a fourth operation 708, into the cavityinterior to provide sound and vibration dampening and to hold the plugsecurely in the second position by surrounding the plug. In a fifthoperation 709, the filler material is heated to cause expansion withinthe interior cavity and completely filling the remaining cavity volumesurrounding the plug. In a sixth operation 710, a badge is attached to arear portion of the club head to cover or occlude the aperture. It isunderstood that the heating operation 709 can be excluded in embodimentsutilizing non-expanding foam such as injection foam, urethane, two partfoam, or chemical initiated expansion foam.

At least one advantage of the embodiments described is that sound isdampened upon impact with a golf ball while maintaining a hollow ironconstruction.

At least another advantage of the embodiments described is that unwantedvibrations can be absorbed by the filler material and plug so that agolfer perceives a softer feel upon impact with the ball.

FIG. 8 illustrates the frequency response function of two example golfclub heads. Examples A and B are similar in construction to theembodiment shown in

FIGS. 6A and 6B. Each example was impacted at center face with a hammerto observe an individual frequency response.

Example B did not include any filler material or plug within theinterior cavity (hereinafter, “unfilled example”). Example A includesthe plug and surrounding filler material, as described above(hereinafter, “filled example”). As shown in FIG. 8 , the first modefrequency response peak 802 of the unfilled example B is noticeablyhigher in comparison to the first mode frequency response peaks 804 ofthe filled example A. Therefore, the accelerance of the unfilled exampleB is higher than the magnitude or amplitude of accelerance of the filledexample A. Thus, the filler material or expanding foam significantlydampens the accelerance amplitude of the filled example A to less thanabout 30 G/N (which is acceleration/input force). The acceleranceamplitude describes the structure's acceleration relative to the inputforce as a function of frequency. In certain embodiments, an accelerancereduction of between about 5% to about 50% between the first modefrequency responses 802,804 of the unfilled example and filled exampleis achieved.

At least another advantage of the embodiments described is that alightweight filler material arrangement is created allowing the centerof gravity of the hollow iron construction to remain low while improvingthe sound and feel of the club during use.

The embodiments described herein conform with the USGA (United StatesGolf Association) Rules of Golf and Appendix II, 5c related to theDetermination of Groove Conformance (issued in August 2008). Forexample, clubs having a loft of 25 degrees or higher meets the groovewidth, groove depth, groove separation, groove consistency, arealimitations, and edge radius requirements set forth by the USGA. In theembodiments described herein, less than 50% of measured values ofArea/(Width+Separation) are greater than 0.0030 in²/in and no singlemeasured value of Area/(Width+Separation) value for any single groove isgreater than 0.0032 in²/in.

With respect to a groove edge radius, the groove edges are in the formof a radius conforming with the USGA Rules of Golf as described by thetwo circles method. In addition, the effective radius is not greaterthan 0.020″. In the embodiments described, less than 50% of the uppergroove edges or lower groove edges fails the two circles method subjectto a 10 degree angular allowance as described in the USGA rules. Nosingle groove edge protrudes more than 0.0003″ outside the outer circle.

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. It will beevident that various modifications may be made thereto without departingfrom the broader spirit and scope of the invention as set forth. Thespecification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

We claim:
 1. A hollow iron-type golf club head comprising: a heelportion, a sole portion, a toe portion, a top-line portion, a frontportion, a rear portion, and a striking face having an unsupported facearea of between about 300 mm² to about 4,000 mm²; a back wall in therear portion enclosing a substantial portion of the rear portion tocreate a substantially enclosed cavity, the enclosed cavity beingdefined by at least a rear surface of the striking face, an inner backwall surface, and the sole portion, at least one plug located within theenclosed cavity, the at least one plug being compressed between the rearsurface of the striking face and the back wall in the rear portion; afiller material located within the enclosed cavity, the filler materialsubstantially surrounding the at least one plug and being configured tohold the at least one plug in place, the golf club head defining anaperture into the enclosed cavity, the aperture being configured toallow the cavity to be filled with the filler material; wherein theunsupported face area includes a thickened central region; wherein theat least one plug is positioned to be in contact with at least a portionof the thickened central region; and wherein the at least one plugoccupies less than 20% of the total club head cavity volume in theenclosed cavity.
 2. The iron-type golf club head of claim 1, wherein theenclosed cavity has a volume between about 1 cc and 200 cc.
 3. Theiron-type golf club head of claim 1, wherein the enclosed cavity has avolume between about 10 cc mid 20 cc.
 4. The iron-type golf club head ofclaim 1, wherein the at least one plug has a volume between about 0.1 ccand about 1 cc.
 5. The iron-type golf club head of claim 1, wherein theat least one plug occupies between about 1% to about 10% of the totalclub head cavity volume in the enclosed cavity.
 6. The iron-type golfclub head of claim 1, wherein the at least one plug occupies betweenabout 0.5% to about 5% of the total club head cavity volume in theenclosed cavity.
 7. The iron-type golf club head of claim 1, wherein thefiller material is an expanding foam material having a density betweenabout 0.03 g/cc and about 0.19 g/cc.
 8. The iron-type golf club head ofclaim 1, wherein the filler material occupies about 50% to about 99% ofthe total club head cavity volume in the enclosed cavity.
 9. Theiron-type golf club head of claim 1, wherein the back wall includes atleast a first aperture, the first aperture being configured to allow theat least one plug to be inserted into the first aperture and isconfigured to allow the at least one plug to move from a first positionto a second position.
 10. The iron-type golf club head of claim 9,wherein the back wall includes at least one slot, the at least one slotbeing connected to the first aperture and is configured to secure the atleast one plug.
 11. A hollow iron-type golf club head comprising: a heelportion, a sole portion, a toe portion, a top-line portion, a frontportion, a rear portion, and a striking face having an unsupported facearea of between about 300 mm² to about 4,000 mm²; a back wall in therear portion enclosing a substantial portion of the rear portion tocreate a substantially enclosed cavity, the enclosed cavity beingdefined by at least a rear surface of the striking, face, an inner backwall surface, and the sole portion; at least one plug located within theenclosed cavity, the at least one plug being compressed between the rearsurface of the striking face and the back wall in the rear portion;wherein the at least one plug occupies less than 20% of the total clubhead cavity volume in the enclosed cavity, and wherein the back wallincludes at least a first aperture, the first aperture being configuredto allow the at least one plug to be inserted into the first apertureand being configured to allow the at least one plug to move from a firstposition to a second position.
 12. The iron-type golf club head of claim11, wherein the enclosed cavity has a volume between about 1 cc and 200cc.
 13. The iron-type golf club head of claim 11, wherein the enclosedcavity has a volume between about 10 cc and 20 cc.
 14. The iron-typegolf club head of claim 11, wherein the at least one plug has a volumebetween about 0.1 cc and about 1 cc.
 15. The iron-type golf club head ofclaim 11, wherein the at least one plug occupies between about 1% toabout 10% of the total club head cavity volume in the enclosed cavity.16. The iron-type golf club head of claim 11, wherein the at least oneplug occupies between about 0.5% to about 5% of the total club headcavity volume in the enclosed cavity.
 17. The iron-type golf club headof claim 11, further comprising a filler material located within theenclosed cavity, the filler material substantially surrounding the atleast one plug and being configured to hold the at least one plug inplace.
 18. The iron-type golf club head of claim 17, wherein the fillermaterial is an expanding foam material having a density between about0.03 g/cc and about 0.19 g/cc.
 19. The iron-type golf club head of claim17, wherein the filler material occupies about 50% to about 99% of thetotal club head cavity volume in the enclosed cavity.
 20. The iron-typegolf club head of claim 17, wherein the filler material completely fillsa remaining cavity volume around the at least one plug.
 21. Theiron-type golf club head of claim 11, wherein the coefficient ofrestitution of the club is greater than about 0.8.
 22. The iron-typegolf club head of claim 11, wherein the back wall includes at least oneslot, the at least one slot being connected to the first aperture and isconfigured to secure the at least one plug.
 23. An iron-type golf clubhead comprising: a heel portion, a toe portion, a top-line portion, asole portion, a striking face having a variable face thickness andjoining the top-line portion to the sole portion, a rear portion joinedto the striking face by the sole portion, and a badge attached to thegolf club head; wherein the rear portion extends upward from the soleportion toward the top-line portion and creates an enclosed cavitybounded by at least a portion of the rear portion, at least a portion ofthe sole portion, at least a portion of the striking face, and at leasta portion of the badge, and a filler material is located within theenclosed cavity; wherein an upper portion of the striking face has afirst thickness and a central region of the striking face has a secondthickness, wherein the second thickness is greater than the firstthickness; wherein a portion of the striking face bounding the enclosedcavity has a face thickness of less than about 3.0 mm; the striking facehas a minimum face thickness of no more than about 2.5 mm, and the solethickness of a portion of the sole portion bounding the enclosed cavityis no more than about 2.0 mm; and wherein a coefficient of restitutionof the club head is greater than about 0.8.
 24. The iron-type golf clubhead of claim 23, wherein the striking face is welded to the club head.25. The iron-type golf club head of claim 24, wherein the enclosedcavity has a volume of 20 cc or less.
 26. The iron-type golf club headof claim 25, wherein the sole portion has a minimum sole portionthickness of no less than 1 mm.
 27. The iron-type golf club head ofclaim 23, wherein the striking face is welded to the club head along aportion of the top-line portion and a portion of the sole portion. 28.The iron-type golf club head of claim 23, wherein the filler materialhas a density of greater than 0.03 g/cc and the filler material weighsless than about 5% of a total club head weight.
 29. The iron-type golfclub head of claim 28, wherein the filler material is a cure-in-placeelastomeric material.
 30. The iron-type golf club head of claim 29,wherein the elastomeric material contains an inorganic filler material.31. The iron-type golf club head of claim 28, wherein the elastomericmaterial is a foamed polymer material.
 32. The iron-type golf club headof claim 28, wherein the elastomeric material is a urethane.
 33. Theiron-type golf club head of claim 28, wherein the elastomeric materialcontains a filler material with a particle size between about 2 μm andabout 90 μm.
 34. The iron-type golf club head of claim 27, wherein therear portion includes a recess located below an ideal impact location,wherein the recess forms a ledge having a length greater than the facethickness.
 35. The iron-type golf club head of claim 28, furtherincluding a weighting element located in the enclosed cavity and incontact with the filler material, wherein the weighting element has agreater density than the face portion.
 36. The iron-type golf club headof claim 28, wherein the filler material has a filler material thicknessmeasured in a front to back direction, and the filler material thicknessis greater below the central region of the striking face than the fillermaterial thickness above the central region of the striking face. 37.The iron-type golf club head of claim 36, wherein an upper portion ofthe enclosed cavity is completely filled with the filler material. 38.The iron-type golf club head of claim 28, wherein the filler materialhas a filler material thickness measured in a front to back direction,and the filler material thickness varies within the enclosed cavity andis greatest proximate the sole portion.
 39. An iron-type golf club headcomprising: a heel portion, a toe portion, a top-line portion, a soleportion, a striking face joining the top-line portion to the soleportion, a rear portion joined to the striking face by the sole portion,and a badge attached to the golf club head; wherein the rear portionextends upward from the sole portion toward the top-line portion andcreates an enclosed cavity bounded at least in part by a portion of therear portion, a portion of the sole portion, and a portion of thestriking face, and a filler material is located within the enclosedcavity; wherein a portion of the sole portion bounding the enclosedcavity has a sole thickness of less than about 2.0 mm; wherein thestriking face has a minimum face thickness of no more than about 2.0 mm;wherein the enclosed cavity has a volume of 20 cc or less; wherein thefiller material occupies no less than 50% of the enclosed cavity, thefiller material weighs less than about 5% of a total club head weight,and the filler material has a density of greater than 0.03 g/cc; andwherein a coefficient of restitution of the club head is greater thanabout 0.8.
 40. The iron-type golf club head of claim 39, wherein theenclosed cavity has an enclosed cavity depth measured in a front to backdirection and the enclosed cavity depth varies.
 41. An iron-type golfclub head comprising: a heel portion, a toe portion, a top-line portion,a sole portion, a striking face having a variable face thickness andjoining the top-line portion to the sole portion, and a rear portionjoined to the striking face by the sole portion; wherein the rearportion extends upward from the sole portion toward the top-line portionand creates a cavity bounded by at least a portion of the rear portion,at least a portion of the sole portion, and at least a portion of thestriking face, and a filler material is located within the cavity;wherein an upper portion of the striking face has a first thickness anda central region of the striking face has a second thickness, whereinthe second thickness is greater than the first thickness and no morethan 3 mm; the striking face has a minimum face thickness of no morethan about 2.5 mm, and the sole thickness of a portion of the soleportion bounding the enclosed cavity is no more than about 2.0 mm; andwherein a coefficient of restitution of the club head is greater thanabout 0.8; wherein the cavity has a cavity depth measured in a front toback direction and the cavity depth varies; wherein the filler materialoccupies weighs less than about 5% of a total club head weight, and thefiller material has a density of greater than 0.03 g/cc; wherein thestriking face is a steel alloy and is welded to the club head; whereinthe cavity has a volume of 20 cc or less.